"N*** analyzed the college roster data of over 1,400 schools across NCAA D1, D2, D3 and NAIA divisions between 2012 and 2017 and found that over 45% of underclassmen athletes are not listed on their college roster the following year."
If we're looking at the same information, the above is a little different than "45% of student-athletes do not return for their sophomore season." Their roster analysis would include medical red-shirts, transfers, cuts, quit playing, quit school, juniors who were drafted, etc.
Still, that % seems really high to me. I'd love to see the raw data.